Radio receiving apparatus



Jan. "28; 1941. G. E. GUSTAFSON 2,229,735.-

- fiAD'Io RECEIVING APPARATUS F iled Se pt. 19, 1940 2 Sheets-Sheet 1 v Y INVENTOR.

BY 6 I /I 7 g MORLEY, J

Jan. 28, 1941. q GUSTAFSQN I 2,229,735

RADIO RECEIVING APPARATUS Fiied Sept. 19. 1940 2 Sheets-Sheet 2 Y L INVENTOR. 6266mm Z? G gem/3907a ATT RNEY.

Patented Jan. 28, 1941 UNITED STATES PATENT OFFICE 2,229,735 RADIO RECEIVING API 'ABATUS Gilbert E. Gustaison, River Forest, 11]., assignor to Zenith Radio Corporation,

corporation of Illinois Chicago, 111., a

Application September 19, 1940, Serial No. 357,441

3 Claims. (Cl. 250-3 3) m maintain, under varying conditions encountered in the use of radio receiving apparatus, the effective inductance and capacitance in the signal receiving circuit at desired and approximately fixed and known values, other than such varia tions therein as may be occasioned by the tuning of said circuit.

A further object is to more accurately maintain the alignment between the tuned signal receiving circuit and the other related tuned cir- 20 cults in radio receiving apparatus.

In the accompanying drawings,

Figure 1 is a rear perspective view of a portable radio set embodying my invention, showing the hinged back panel of the casing thereof in 2 open position to disclose the arrangement of the loop antenna unit and the disposal of the an-' tenna connecting lead-member when the antenna is to be used within the casing, and illustrating the convenient placement of the switch so employed in this embodiment of my invention;

Figure 2 is a vertical sectional view, upon an enlarged scale, taken upon the line 2-2 of Figure 1, showing indetail the construction of a simple form of circuit selecting switch which 35 may be used to connect and disconnect other elements comprised in my invention;

Figure 3 is a horizontal sectional view, upon an enlarged scale, taken on the line 33 of Figure 1, showing in detail the construction of the switch and indicating the operation thereof and Figure 4 is a schematic diagram of the antenna circuit arranged according to this embodiment of my invention.

5 While the invention is herein illustrated and described as embodied in a compactly arranged portable radio receiving'set having a loop antenna which may be housed and used within the casing thereof or removed and individually supported apart therefrom, it is to be understood that the usefulness of the invention is not limited to portable receivers or to the particular type of antenna herein shown.

Popular demand requires that commercial ra- 55 die receiving apparatus be of the single-control tuner type. This means that all the circuits which are to be tuned in selecting the desired signal must be kept in tracking alignment. This is comparatively easy to effect in all of the circuits with the exception of the circuit of which 5 the antenna is a part. By nature necessarily exposed to the influence of extrinsic interferences and disturbances, the antenna, introduces such unpredictable interferences and disturbances in the antenna circuit regardless of its own char- A acteristics. However, where the inductance, capacitance, and resistance characteristics of the antenna itself are subjected to disturbances which can be anticipated, as I shall hereinafter describe, it is highly desirable that provision be made to prevent such intrinsicdisturbances from affecting the antenna circuit as far as possible.

In order that my invention may be clearly understood, it may be well to mention that, in properly designed radio receiving apparatus, maintenance of the. highest degree of efficiency requires the retention of the inductance, capacitance, and -resistance 'valuesof the antenna circuit as they were originally computed and tested by the designer of the apparatus of which such circuit is a most important part, so that the ,original alignment, selectivity, and high signal output of the antenna circuit may be preserved. Correct alignment is necessary in order'to obtain high selectivity and high signal output, and ,30 all of these are factors in obtaining a high rejection of what are known asimage and ghost signals. The advantages obtainable from high selectivity and high signal output of the antenna circuit are generally well known to those familiar with the art. For example, high signal output from ,the'antenna circuit necessitates less amplification for a given speaker; ,volume. Consequently. less power is required and often fewer stages of amplification are necessary. It is also possible to use a much smaller antenna where provision is made to maintain high signal output values. These factors are particularly important --if weight or the overall size of the apparatus are restricted, as they are in the designing of portable receivers such as shown in the accompanying drawings. Furthermore, the maintenance of high outputvalues in the antenna circuit in the manner hereinafter described results in a high signal-to-internal-noise ratio.

If the design and arrangement of the antenna may be established, it is relatively simple to determine the values of its resitance, inductance and capacitance and to design the radio receiving apparatus accordingly. However, this inven- 5 cabinet thereof.

' the variation. Therefore, by definition,

2 tion contemplates allowing the user relative freedom in locating the antenna in relation to the radio receiving apparatus, and in relation to objects extrinsic to the apparatus, in order to meet the varying conditions which may be encountered.

It is well known to those familiar with the art that the capacitance and inductance of an antenna are greatly affected by surrounding objects. This is especially so in radio apparatus having a loop antenna, since the loop antenna is an inductance unit itself and is part of a tuned circuit, therefore changes in the positioning of the loop antenna with respect to adjacent objects may effect changes in its inductance or capacitance, and may seriously disturb not only its characteristics but those of the circuit of which the loop antenna is a part.

Modern types of portable radio receiving sets are provided with loop antennae, and it has been found highly desirable to construct the loop antennae of such sets as removable units, provide them with connecting lead-members of some length, and in each case design and arrange the antenna, ceiving apparatus so that the antenna may be used within the casing of the set or individually supported some distance from the set. One of the reasons for doing this is to permit the receiving apparatus to be used within a signal shielding structure and allow the antenna to be placed in or near a window or opening in said structure.

As may be readily seen, extending the field of use of an extendible loop antenna also extends the field of influencing conditions to which the antenna may .be subjected, and, when an extendible loop antenna is part of portable radio receiving apparatus, the iield of influencing conditions is even further extended. For example, the portable apparatus may be used in an aeroplane or in a railroad car, with the antenna placed within the window of such plane or car. The portable apparatus may also be used in any signal shielding structure, with the antenna placed at or near an opening in such structure. Moreover, the portable apparatus will often .be used with the antenna in As is well known, the effect on the inductance and capacitance of the antenna by an extrinsic body depends on the size of said body, rial of which it is constructed, and the placement of the antenna with relation thereto. Variations in these factors might, in radio receiving apparatus using multiple control tuning means, be exactly compensated for if the operator were experienced. In the single control type, this is impossible, as single control indicates tuning a combination ofvtwo or more circuits with a single control means, and if one circuit of the combination varies from alignment with another thereof, additional means must be used for correcting the tuning would no longer be by a single control means.

It has been found that there are a number of definable major situations under which notable changes are effected in the inductance and capacitance of the antenna, and that situations other than these result only in slight variations in some one of the major situations. Y

The number of major situations herein considered is based upon the different uses to which the radio receiving apparatus may be put, and upon the type of radio receiving apparatus used. For portable radio receiving apparatus provided the lead-member, and the radio re-.'

position within the the mate-.

with an extendible antenna and of the type usually sold to the general public for the reception of commercial programs. it has been found that three situations cover the major inductance and capacitance changes.-

These three situations may be described as follows: The first is characterized by the placement of the antenna and the antenna'connecting member in the casing of the apparatus. In the second, the antenna is extended but not placed in immediate proximity to a current-carrying metallic object. In the third, the antenna is extended and placed in close proximity to a current-carrying metallic object or metal-surrounded aperture in a shielding structure, such as the window of a plane or railroad car.

The inductance changes in the first and third mentioned situations are very similar. The close proximity to the metal, either of the metal window frame (as in situation three) or the chassis of the apparatus (as in situation one), lowers the inductance of the antenna, as compared to situation two. The conditions which materially change the capacitance of the antenna and the antenna circuit are unchanged in the second and third mentioned situations. It has been found that the capacitance is lower when the antenna and the antenna connecting lead are positioned within the casing than when they are removed and extended therefrom. Therefore the capacitance of the antenna and the antenna circuit is lower in situation one than in situations two or three.

One means of carrying out my invention is shown in the accompanying drawings, in which the antenna is indicated by reference numeral I in Figures 1 and 4,'and the antennaconnecting member by reference numeral 2. The antenna connecting member enters the chassis 3 of the radio apparatus as indicated at l. The switch Ii in Figure l is shown in greater detail in Figures 2 and 3. The contacts 8, I and 8 of the switch 5 are shown in Figures 3 and 4. Also shown in Figures 2 and 3, is a ball member 9, operable to connect the contacts 8 and I or 'I and 8. The

ball member 9 is shown schematically in Figure 4 in three possible positions, namely a, a, a". lit and Ii are the. tuning condenser and trimming condenser, respectively; i2 and I3 indicate two inductance coils; It indicates the condenser of the compensating device; [I the grid of the first tube of the radio receiving apparatus; and I! the connection to ground.

Other means vthan the switch shown may be used to control the circuit. It is possible, for example, to employ the well-known phone-jack plug-and-socket connections. Then the choice of sockets would be similar to the choice of positions of the three-position switch herein shown.

The operation of my invention is as follows: The ball member 8, when placed in the position indicated by a in Figure 4, connects the compensating condenser it into the circuit, in parallel with the tuning and trimming condensers, l0 and ii, thereby conditioning the antenna circuit for the first of the situations previously described, the extra capacitance It being added, since, as previously mentioned, the capacitance of the antenna and the antenna circuit is lower in situation one than in situations two or'three.

When the ball member I is in position a, the condenser i4 and the inductance unit it are not in the circuit, and the circuit is adjusted for the second previously mentioned situation, wherein the antenna is extended but not placed in ininiediate proximity to a current-carrying metallic object, the inductance of the antenna and the antenna connecting lead being normal.

When the ball member 9 is in position a", the circuit is adjusted for the third previously mentioned situation, both inductance units [2 and I3 are in the circuit, as they were in situation one, the proximity of the loop antenna to a currentcarrying metallic body being somewhat similar, but condenser is not in the circuit, since the loop antenna is in extended position away from thechassis of the apparatus: i

Having fully described my invention" and the mannerof its use,Iclaim-j I I 1 1. In radio receiving apparatus, the combinatio'n', with a-tunable antenna circuit comprising an antenna variably positionable at will with re-' spect to ,said apparatus, and an'antenna lead connecting said antenna with said apparatus,

wherein changes in the and antenna lead with positions of said'antenn'a cult, ,of means acting upon connection with said circuit to compensate for such variations comprising a capacitance element and adjustable means operable to connect said element with and disconnect it from said circuit at will. I

2. In radio receiving apparatus, the'combination, with a tunable antenna circuit comprising an antenna variably positionable'atwill apart from said apparatus upon connection with said circuit to respect to said apparatus eflect variations in the characteristics of said cir- I saidinductance and with respect to objects H having an inductive effect upon said antenna, and an antenna lead connecting said antenna with said apparatus, wherein changes in the positions of said antenna and antenna lead with respect to said objects effect variations in the characteristics of said circuit, of means acting compensate for such variations comprising an inductance element and adjustable means operable to connect said element'withand disconnect it from said circuit, at will.

3. In radio-receiving apparatus, the combina- .tion, with a tunable antennacircuit comprising an antenna variablypositionable at will both with respect tonsaidapparatus' and apart from said-apparatusiwith' respect to objects having an I I inductive efiect'upon said antenna, and, an'an-,

tenna lead connecting said antenna with said "apparatus, wherein changes in the positions of said antenna and antennalead both with respect -to said apparatus "and'apart from said apparatus' with respect to saidother objects effect variations' in the characteristics of said circuit; of a I capacitance element and an inductance element each acting upon connection with and disconnection from said circuit to compensate for such variations, and adjustable means operable at will to simultaneously effect the connection of said capacitance element and the disconnection 0! element with and from said circuit and'vice versa. h V

Y GILBERT E'.,GUSTAFSON. 

